Optical electric field enhancing devices using the electric field enhancing effect of the localized plasmon resonance phenomenon on the surface of a metal have been known. With such an optical electric field enhancing device, when light is applied to a metal body, in particular, a metal body having nano-order protrusions and recesses on the surface, which is in contact with a sample, the optical electric fields on the surface are enhanced due to the localized plasmon resonance. When the optical electric field enhancing device is applied as a carrier (substrate) for carrying an analyte in a measuring apparatus which identifies and/or quantifies the analyte based on optical properties of signal light that is emitted from the analyte when light is applied, the signal light can be enhanced by the enhanced electric fields and highly sensitive measurement can be performed.
As a measuring method using the optical electric field enhancing device, surface enhanced Raman spectroscopy (SERS) is well known (see S. Ghadarghadr et al., “Plasmonic array nanoantennas on layered substrates: modeling and radiation characteristics”, Optics Express, Vol. 17, No. 21, pp. 18556-18570, 2009, hereinafter Non-Patent Literature 1). The Raman spectroscopy is a method to obtain a spectrum (Raman spectrum) of Raman-scattered light by separating scattered light which is obtained by applying single wavelength light to a material, and is used to identify a material by detecting a Raman shift, to measure the concentration of an analyte in a sample based on Raman spectrum intensity, etc.
As the optical electric field enhancing device, a substrate which is formed by forming protrusions and recesses on the surface of a Si substrate and forming a metal film on the surface of the protrusions and recesses is mainly used (see PCT Japanese Publication No. 2006-514286, Japanese Patent No. 4347801, and Japanese Unexamined Patent Publication No. 2006-145230, hereinafter Patent Literature 1, 2, and 3, respectively).
Also, a substrate which is formed by anodizing a surface of an Al substrate to partially form a metal oxide layer (Al2O3), and filling a plurality of fine holes which are naturally formed in the surface of the metal oxide layer during the anodization with a metal has been proposed (see Japanese Unexamined Patent Publication No. 2005-172569, hereinafter Patent Literature 4).
Further, the present inventors have disclosed an optical electric field enhancing device wherein the surface of protrusions and recesses of a transparent fine uneven structure called boehmite is covered with a metal film, which optical electric field enhancing device allows detecting enhanced signal light at good S/N without the signal light being blocked by the sample when the sample is a μm-order or larger sample, such as cells (see Japanese Unexamined Patent Publication Nos. 2012-063293 and 2012-063294, hereinafter Patent Literature 5 and 6, respectively).
According to this optical electric field enhancing device, the enhanced signal light can be detected from the rear surface side (the opposite surface from the surface carrying the sample) of the device, and this allows detecting the signal light enhanced by the enhanced optical electric fields without being blocked by the analyte.
On the other hand, a chemical imaging technique which performs multi-point measurement by scanning a sample on a carrier at regular point intervals (spatial resolution) and visualizes the results of the measurement to display a planar distribution image (map) is known. The chemical imaging allows intuitive understanding of distribution of components in the in-plane direction of the sample. Japanese Unexamined Patent Publication Nos. 2000-055809 and 2007-147357 (hereinafter, Patent Literature 7 and 8) have disclosed Raman spectrum imaging.